Recent experiments show that anti mouse immunoglobulin (Ig) becomes strongly mitogenic for mouse B lymphocytes in vitro when coupled covalently to the surface of polyacrylamide beads. Mouse spleen cells stimulated by these anti Ig beads proliferate but do not go on the high rate Ig synthesis and secretion, as shown by a reverse hemolytic plaque assay using sheep red cells coated with anti mouse Ig. I propose to use this system to investigate the cell surface events in B lymphocyte activation and the subsequent surface events and intercellular signals which regulate proliferation versus differentiation to antibody secretion. An integral part of this investigation will be the characterization of mouse B lymphocyte subsets which may differ from one another in their susceptibility to or dependence upon various inductive and regulatory signals. Similar experiments are underway with human peripheral blood lymphocytes in an attempt to distinguish separate effects of surface IgM and IgD on the lymphocyte response. BIBLIOGRAPHIC REFERENCE: Parker, D.C., "Stimulation of mouse and Human B lymphocytes by Class-specific Insoluble Anti-Immunoglobulins", J. of Supramolecular Structure, Supplement, (1977) p. 219 abstract.